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<FONT color="green">001</FONT>    /*<a name="line.1"></a>
<FONT color="green">002</FONT>     * Licensed to the Apache Software Foundation (ASF) under one or more<a name="line.2"></a>
<FONT color="green">003</FONT>     * contributor license agreements.  See the NOTICE file distributed with<a name="line.3"></a>
<FONT color="green">004</FONT>     * this work for additional information regarding copyright ownership.<a name="line.4"></a>
<FONT color="green">005</FONT>     * The ASF licenses this file to You under the Apache License, Version 2.0<a name="line.5"></a>
<FONT color="green">006</FONT>     * (the "License"); you may not use this file except in compliance with<a name="line.6"></a>
<FONT color="green">007</FONT>     * the License.  You may obtain a copy of the License at<a name="line.7"></a>
<FONT color="green">008</FONT>     *<a name="line.8"></a>
<FONT color="green">009</FONT>     *     http://www.apache.org/licenses/LICENSE-2.0<a name="line.9"></a>
<FONT color="green">010</FONT>     *<a name="line.10"></a>
<FONT color="green">011</FONT>     * Unless required by applicable law or agreed to in writing, software<a name="line.11"></a>
<FONT color="green">012</FONT>     * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.12"></a>
<FONT color="green">013</FONT>     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.13"></a>
<FONT color="green">014</FONT>     * See the License for the specific language governing permissions and<a name="line.14"></a>
<FONT color="green">015</FONT>     * limitations under the License.<a name="line.15"></a>
<FONT color="green">016</FONT>     */<a name="line.16"></a>
<FONT color="green">017</FONT>    package org.apache.commons.configuration.interpol;<a name="line.17"></a>
<FONT color="green">018</FONT>    <a name="line.18"></a>
<FONT color="green">019</FONT>    import java.lang.reflect.Field;<a name="line.19"></a>
<FONT color="green">020</FONT>    import java.util.HashMap;<a name="line.20"></a>
<FONT color="green">021</FONT>    import java.util.Map;<a name="line.21"></a>
<FONT color="green">022</FONT>    <a name="line.22"></a>
<FONT color="green">023</FONT>    import org.apache.commons.lang.ClassUtils;<a name="line.23"></a>
<FONT color="green">024</FONT>    import org.apache.commons.lang.text.StrLookup;<a name="line.24"></a>
<FONT color="green">025</FONT>    import org.apache.commons.logging.Log;<a name="line.25"></a>
<FONT color="green">026</FONT>    import org.apache.commons.logging.LogFactory;<a name="line.26"></a>
<FONT color="green">027</FONT>    <a name="line.27"></a>
<FONT color="green">028</FONT>    /**<a name="line.28"></a>
<FONT color="green">029</FONT>     * &lt;p&gt;<a name="line.29"></a>
<FONT color="green">030</FONT>     * A specialized lookup implementation that allows access to constant fields of<a name="line.30"></a>
<FONT color="green">031</FONT>     * classes.<a name="line.31"></a>
<FONT color="green">032</FONT>     * &lt;/p&gt;<a name="line.32"></a>
<FONT color="green">033</FONT>     * &lt;p&gt;<a name="line.33"></a>
<FONT color="green">034</FONT>     * Sometimes it is necessary in a configuration file to refer to a constant<a name="line.34"></a>
<FONT color="green">035</FONT>     * defined in a class. This can be done with this lookup implementation.<a name="line.35"></a>
<FONT color="green">036</FONT>     * Variable names passed in must be of the form<a name="line.36"></a>
<FONT color="green">037</FONT>     * {@code mypackage.MyClass.FIELD}. The {@code lookup()} method<a name="line.37"></a>
<FONT color="green">038</FONT>     * will split the passed in string at the last dot, separating the fully<a name="line.38"></a>
<FONT color="green">039</FONT>     * qualified class name and the name of the constant (i.e. &lt;strong&gt;static final&lt;/strong&gt;)<a name="line.39"></a>
<FONT color="green">040</FONT>     * member field. Then the class is loaded and the field's value is obtained<a name="line.40"></a>
<FONT color="green">041</FONT>     * using reflection.<a name="line.41"></a>
<FONT color="green">042</FONT>     * &lt;/p&gt;<a name="line.42"></a>
<FONT color="green">043</FONT>     * &lt;p&gt;<a name="line.43"></a>
<FONT color="green">044</FONT>     * Once retrieved values are cached for fast access. This class is thread-safe.<a name="line.44"></a>
<FONT color="green">045</FONT>     * It can be used as a standard (i.e. global) lookup object and serve multiple<a name="line.45"></a>
<FONT color="green">046</FONT>     * clients concurrently.<a name="line.46"></a>
<FONT color="green">047</FONT>     * &lt;/p&gt;<a name="line.47"></a>
<FONT color="green">048</FONT>     *<a name="line.48"></a>
<FONT color="green">049</FONT>     * @version $Id: ConstantLookup.java 1210218 2011-12-04 20:57:48Z oheger $<a name="line.49"></a>
<FONT color="green">050</FONT>     * @since 1.4<a name="line.50"></a>
<FONT color="green">051</FONT>     * @author &lt;a<a name="line.51"></a>
<FONT color="green">052</FONT>     * href="http://commons.apache.org/configuration/team-list.html"&gt;Commons<a name="line.52"></a>
<FONT color="green">053</FONT>     * Configuration team&lt;/a&gt;<a name="line.53"></a>
<FONT color="green">054</FONT>     */<a name="line.54"></a>
<FONT color="green">055</FONT>    public class ConstantLookup extends StrLookup<a name="line.55"></a>
<FONT color="green">056</FONT>    {<a name="line.56"></a>
<FONT color="green">057</FONT>        /** Constant for the field separator. */<a name="line.57"></a>
<FONT color="green">058</FONT>        private static final char FIELD_SEPRATOR = '.';<a name="line.58"></a>
<FONT color="green">059</FONT>    <a name="line.59"></a>
<FONT color="green">060</FONT>        /** An internally used cache for already retrieved values. */<a name="line.60"></a>
<FONT color="green">061</FONT>        private static Map&lt;String, String&gt; constantCache = new HashMap&lt;String, String&gt;();<a name="line.61"></a>
<FONT color="green">062</FONT>    <a name="line.62"></a>
<FONT color="green">063</FONT>        /** The logger. */<a name="line.63"></a>
<FONT color="green">064</FONT>        private Log log = LogFactory.getLog(getClass());<a name="line.64"></a>
<FONT color="green">065</FONT>    <a name="line.65"></a>
<FONT color="green">066</FONT>        /**<a name="line.66"></a>
<FONT color="green">067</FONT>         * Tries to resolve the specified variable. The passed in variable name is<a name="line.67"></a>
<FONT color="green">068</FONT>         * interpreted as the name of a &lt;b&gt;static final&lt;/b&gt; member field of a<a name="line.68"></a>
<FONT color="green">069</FONT>         * class. If the value has already been obtained, it can be retrieved from<a name="line.69"></a>
<FONT color="green">070</FONT>         * an internal cache. Otherwise this method will invoke the<a name="line.70"></a>
<FONT color="green">071</FONT>         * {@code resolveField()} method and pass in the name of the class<a name="line.71"></a>
<FONT color="green">072</FONT>         * and the field.<a name="line.72"></a>
<FONT color="green">073</FONT>         *<a name="line.73"></a>
<FONT color="green">074</FONT>         * @param var the name of the variable to be resolved<a name="line.74"></a>
<FONT color="green">075</FONT>         * @return the value of this variable or &lt;b&gt;null&lt;/b&gt; if it cannot be<a name="line.75"></a>
<FONT color="green">076</FONT>         * resolved<a name="line.76"></a>
<FONT color="green">077</FONT>         */<a name="line.77"></a>
<FONT color="green">078</FONT>        @Override<a name="line.78"></a>
<FONT color="green">079</FONT>        public String lookup(String var)<a name="line.79"></a>
<FONT color="green">080</FONT>        {<a name="line.80"></a>
<FONT color="green">081</FONT>            if (var == null)<a name="line.81"></a>
<FONT color="green">082</FONT>            {<a name="line.82"></a>
<FONT color="green">083</FONT>                return null;<a name="line.83"></a>
<FONT color="green">084</FONT>            }<a name="line.84"></a>
<FONT color="green">085</FONT>    <a name="line.85"></a>
<FONT color="green">086</FONT>            String result;<a name="line.86"></a>
<FONT color="green">087</FONT>            synchronized (constantCache)<a name="line.87"></a>
<FONT color="green">088</FONT>            {<a name="line.88"></a>
<FONT color="green">089</FONT>                result = constantCache.get(var);<a name="line.89"></a>
<FONT color="green">090</FONT>            }<a name="line.90"></a>
<FONT color="green">091</FONT>            if (result != null)<a name="line.91"></a>
<FONT color="green">092</FONT>            {<a name="line.92"></a>
<FONT color="green">093</FONT>                return result;<a name="line.93"></a>
<FONT color="green">094</FONT>            }<a name="line.94"></a>
<FONT color="green">095</FONT>    <a name="line.95"></a>
<FONT color="green">096</FONT>            int fieldPos = var.lastIndexOf(FIELD_SEPRATOR);<a name="line.96"></a>
<FONT color="green">097</FONT>            if (fieldPos &lt; 0)<a name="line.97"></a>
<FONT color="green">098</FONT>            {<a name="line.98"></a>
<FONT color="green">099</FONT>                return null;<a name="line.99"></a>
<FONT color="green">100</FONT>            }<a name="line.100"></a>
<FONT color="green">101</FONT>            try<a name="line.101"></a>
<FONT color="green">102</FONT>            {<a name="line.102"></a>
<FONT color="green">103</FONT>                Object value = resolveField(var.substring(0, fieldPos), var<a name="line.103"></a>
<FONT color="green">104</FONT>                        .substring(fieldPos + 1));<a name="line.104"></a>
<FONT color="green">105</FONT>                if (value != null)<a name="line.105"></a>
<FONT color="green">106</FONT>                {<a name="line.106"></a>
<FONT color="green">107</FONT>                    synchronized (constantCache)<a name="line.107"></a>
<FONT color="green">108</FONT>                    {<a name="line.108"></a>
<FONT color="green">109</FONT>                        // In worst case, the value will be fetched multiple times<a name="line.109"></a>
<FONT color="green">110</FONT>                        // because of this lax synchronisation, but for constant<a name="line.110"></a>
<FONT color="green">111</FONT>                        // values this shouldn't be a problem.<a name="line.111"></a>
<FONT color="green">112</FONT>                        constantCache.put(var, String.valueOf(value));<a name="line.112"></a>
<FONT color="green">113</FONT>                    }<a name="line.113"></a>
<FONT color="green">114</FONT>                    result = value.toString();<a name="line.114"></a>
<FONT color="green">115</FONT>                }<a name="line.115"></a>
<FONT color="green">116</FONT>            }<a name="line.116"></a>
<FONT color="green">117</FONT>            catch (Exception ex)<a name="line.117"></a>
<FONT color="green">118</FONT>            {<a name="line.118"></a>
<FONT color="green">119</FONT>                log.warn("Could not obtain value for variable " + var, ex);<a name="line.119"></a>
<FONT color="green">120</FONT>            }<a name="line.120"></a>
<FONT color="green">121</FONT>    <a name="line.121"></a>
<FONT color="green">122</FONT>            return result;<a name="line.122"></a>
<FONT color="green">123</FONT>        }<a name="line.123"></a>
<FONT color="green">124</FONT>    <a name="line.124"></a>
<FONT color="green">125</FONT>        /**<a name="line.125"></a>
<FONT color="green">126</FONT>         * Clears the shared cache with the so far resolved constants.<a name="line.126"></a>
<FONT color="green">127</FONT>         */<a name="line.127"></a>
<FONT color="green">128</FONT>        public static void clear()<a name="line.128"></a>
<FONT color="green">129</FONT>        {<a name="line.129"></a>
<FONT color="green">130</FONT>            synchronized (constantCache)<a name="line.130"></a>
<FONT color="green">131</FONT>            {<a name="line.131"></a>
<FONT color="green">132</FONT>                constantCache.clear();<a name="line.132"></a>
<FONT color="green">133</FONT>            }<a name="line.133"></a>
<FONT color="green">134</FONT>        }<a name="line.134"></a>
<FONT color="green">135</FONT>    <a name="line.135"></a>
<FONT color="green">136</FONT>        /**<a name="line.136"></a>
<FONT color="green">137</FONT>         * Determines the value of the specified constant member field of a class.<a name="line.137"></a>
<FONT color="green">138</FONT>         * This implementation will call {@code fetchClass()} to obtain the<a name="line.138"></a>
<FONT color="green">139</FONT>         * {@code java.lang.Class} object for the target class. Then it will<a name="line.139"></a>
<FONT color="green">140</FONT>         * use reflection to obtain the field's value. For this to work the field<a name="line.140"></a>
<FONT color="green">141</FONT>         * must be accessable.<a name="line.141"></a>
<FONT color="green">142</FONT>         *<a name="line.142"></a>
<FONT color="green">143</FONT>         * @param className the name of the class<a name="line.143"></a>
<FONT color="green">144</FONT>         * @param fieldName the name of the member field of that class to read<a name="line.144"></a>
<FONT color="green">145</FONT>         * @return the field's value<a name="line.145"></a>
<FONT color="green">146</FONT>         * @throws Exception if an error occurs<a name="line.146"></a>
<FONT color="green">147</FONT>         */<a name="line.147"></a>
<FONT color="green">148</FONT>        protected Object resolveField(String className, String fieldName)<a name="line.148"></a>
<FONT color="green">149</FONT>                throws Exception<a name="line.149"></a>
<FONT color="green">150</FONT>        {<a name="line.150"></a>
<FONT color="green">151</FONT>            Class&lt;?&gt; clazz = fetchClass(className);<a name="line.151"></a>
<FONT color="green">152</FONT>            Field field = clazz.getField(fieldName);<a name="line.152"></a>
<FONT color="green">153</FONT>            return field.get(null);<a name="line.153"></a>
<FONT color="green">154</FONT>        }<a name="line.154"></a>
<FONT color="green">155</FONT>    <a name="line.155"></a>
<FONT color="green">156</FONT>        /**<a name="line.156"></a>
<FONT color="green">157</FONT>         * Loads the class with the specified name. If an application has special<a name="line.157"></a>
<FONT color="green">158</FONT>         * needs regarding the class loaders to be used, it can hook in here. This<a name="line.158"></a>
<FONT color="green">159</FONT>         * implementation delegates to the {@code getClass()} method of<a name="line.159"></a>
<FONT color="green">160</FONT>         * Commons Lang's<a name="line.160"></a>
<FONT color="green">161</FONT>         * &lt;code&gt;&lt;a href="http://commons.apache.org/lang/api-release/org/apache/commons/lang/ClassUtils.html"&gt;<a name="line.161"></a>
<FONT color="green">162</FONT>         * ClassUtils&lt;/a&gt;&lt;/code&gt;.<a name="line.162"></a>
<FONT color="green">163</FONT>         *<a name="line.163"></a>
<FONT color="green">164</FONT>         * @param className the name of the class to be loaded<a name="line.164"></a>
<FONT color="green">165</FONT>         * @return the corresponding class object<a name="line.165"></a>
<FONT color="green">166</FONT>         * @throws ClassNotFoundException if the class cannot be loaded<a name="line.166"></a>
<FONT color="green">167</FONT>         */<a name="line.167"></a>
<FONT color="green">168</FONT>        protected Class&lt;?&gt; fetchClass(String className) throws ClassNotFoundException<a name="line.168"></a>
<FONT color="green">169</FONT>        {<a name="line.169"></a>
<FONT color="green">170</FONT>            return ClassUtils.getClass(className);<a name="line.170"></a>
<FONT color="green">171</FONT>        }<a name="line.171"></a>
<FONT color="green">172</FONT>    }<a name="line.172"></a>




























































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